To meet the demand for wireless data traffic having increased since deployment of 4G (4th-Generation) communication systems, efforts have been made to develop an improved 5G (5th-Generation) or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a ‘beyond 4G network’ or a ‘post LTE system’.
The 5G communication system is considered to be implemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To decrease propagation loss of the radio waves and increase the transmission distance, the beamforming, massive multiple-input multiple-output (MIMO), full dimensional MIMO (FD-MIMO), array antenna, an analog beam forming, large scale antenna techniques are discussed in 5G communication systems.
In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud radio access networks (RANs), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, coordinated multi-points (CoMP), reception-end interference cancellation and the like.
In the 5G system, hybrid FSK and QAM modulation (FQAM) and sliding window superposition coding (SWSC) as an advanced coding modulation (ACM), and filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) as an advanced access technology have been developed.
Accompanying with increasing sharp contradiction between outbreak of users' demands for high-bandwidth wireless services and scarce spectrum resources, mobile operators start to consider taking free licensed frequency bands (which may also be referred to as unlicensed frequency bands) as a supplement for licensed frequency bands. Thus, research about deploying long term evolution (LTE) on unlicensed frequency bands has been scheduled. Third generation partnership project (3GPP) starts to research how to effectively improve the whole network frequency utilization, by performing an effective carrier aggregation on unlicensed frequency bands and licensed frequency bands, on the precondition that there is no significant impact on other technologies of unlicensed frequency bands. FIG. 1 is a schematic diagram illustrating a mutual networking scene of licensed frequency bands and unlicensed frequency bands.
Unlicensed frequency bands have generally been allocated for other applications, e.g., wireless fidelity (WiFi) of radar or 802.11 series. Thus, interference level on unlicensed frequency bands is uncertain. Subsequently, it is generally difficulty to guarantee quality of service (QoS) of LTE transmission. However, the unlicensed frequency bands may still be applied for data transmission with lower QoS requirements. Here, an LTE system deployed on the unlicensed frequency bands may be referred to as a license assisted access (LAA) system. How to avoid mutual interference between the LAA system and other wireless systems, such as radar, or WiFi, on the unlicensed frequency bands is a key problem. Clear channel assessment (CCA), which is a mechanism to avoid collision, is generally employed by the unlicensed frequency bands. Before transmitting a signal, a station (STA) must detect a wireless channel. When detecting that the wireless channel is idle, the STA may occupy the wireless channel and transmit the signal. The LAA system also needs to comply with a similar mechanism, so as to ensure a small interference to other signals. A simpler method is as follows. An LAA device (base station or terminal) may be dynamically opened or closed, based on a CCA result. That is, when detecting that a channel is idle, the LAA device may transmit a signal. When detecting that a channel is busy, the LAA device may not transmit a signal. In the LAA system, uplink transmission of a UE is still scheduled by a base station. When scheduling an uplink signal of a UE, a base station cannot predict whether the uplink signal of the UE can be transmitted in a scheduled subframe, due to different interferences suffered by the base station and the UE in different geographical locations. Besides, when receiving a subframe indicating the scheduling information, the UE also cannot predict whether there is an idle channel in the scheduled subframe, so as to transmit an uplink signal. When a UE works in a carrier aggregation mode, the uplink maximum transmission power is relevant with number of uplink carriers transmitted simultaneously. Since uplink transmission of carriers in the unlicensed frequency bands may not be determined before scheduling a subframe, in a more extreme case, the uplink transmission of carriers in the unlicensed frequency bands may be determined at the start edge of the scheduled subframe, the UE may determine a corresponding maximum uplink transmission power at the start edge of the scheduled subframe. That is, the UE cannot determine the maximum uplink transmission power in advance, and cannot determine whether the uplink transmission power controlled by the base station exceeds the maximum uplink transmission power, so as to allocate a corresponding power, e.g., reduce power of an uplink channel/signal with a lower priority. Besides, under the circumstances that not all the starting points of uplink subframes of carriers in the unlicensed frequency bands are aligned, for example, multiple carriers respectively belong to different timing advance groups (TAGs), when allocating power for a carrier with an earlier starting point of uplink subframe, the UE cannot determine whether a later carrier in the unlicensed frequency bands can be transmitted. Subsequently, the UE cannot determine whether it is necessary to reserve power for these later carriers. The foregoing is totally different from power adjustment in current LTE system. In the current LTE system, when receiving uplink scheduling information, a UE may determine total configured maximum output power PCMAX and/or configured maximum output power of each carrier PCMAX,c. UE can determine whether it would be power limited and how to allocate the power. Thus, the UE has sufficient time to prepare for power allocation and transmission, e.g., the time is greater than 2 ms.